See instructions): This is a competitive renewal of a training program in Developmental Hematology in the Department of Pediatrics at Washington University School of Medicine. The program will provide pediatric physicians (M.D.'s or M.D., Ph.D.'s) with postdoctoral research experience with the long-term goal of producing independent investigators capable of making important contributions to biomedical research. The program will support one second-year (PGY-4) and one third-year fellow (PGY-5) each year. The trainees will be recruited from the Hematology-Oncology fellowship program in the Department of Pediatrics at Washington University School of Medicine. The fellowship program is comprised of three to four years of training, only two of which will be supported by the T32. The Hematology-Oncology fellowship includes many qualified applicants with backgrounds in hematology research. Trainees will participate in a formal seminar series that includes a discussion of current research in developmental hematology, along with didactic sessions in statistics, design of research, and the ethical conduct of research. Trainees may perform their postdoctoral research in a wide range of laboratories at Washington University, provided the research is relevant to the field of'developmental hematology. Alan L. Schwartz, M.D., Ph.D., will serve as Program Director. The continued support of this program will help to close the gap between basic developmental biologists and pediatrician clinicians. RELEVANCE (See instructions): This training program is designed to bridge the gap between clinical and basic scientists. The focus of this program is the training of physician scientists in basic and applied research relevant to the causes of hematologic diseases in children. Qualified trainees, both MDs and MD/PhDs, will be selected for their potential to assume academic positions in pediatric departments at major medical schools. The training program compliments existing programs in the Department of Pediatrics designed to enhance training in developmental biology and animal models of disease.